I don't know why this went wrong, any thoughts appreciated.
Here's a pic of both sides the negs: http://www.londondailyphoto.com/images/IMG_2349.JPG

I normally process TMax (Tmax400 in this case) in T-Max Dev but as I had some D-76 left at the end of it's life, I used that. To be exact, I had about 800ml of D76 mixed 6 weeks ago, used once 5 minutes before to process a roll of Fuji Acros (perfect) I poured the 500ml from the Acros dev back into the container and used 500ml of that in the tank. 20.5oC, 7 min 10 s, Ilford rapid fixer - (end of use, too, but I didn't think it was exhausted).

Unfortunately, I always take care with times and chemicals so I've had no experience of failure, and I don't know what's happened. Any ideas?